Abstract
Carotene was obtained from a methyl alcohol solution of the unsaponifiable fraction of the lipids of lettuce. After recrystallization from petroleum ether, the melting point was 179.5-180°. 200 mg. were obtained from approximately 150 kilos of fresh lettuce.
The crystal form differs depending on the solvent from which it is crystallized: from petroleum ether, rhombohedrons; chloroform and methyl alcohol, needles; carbon disulfide and absolute alcohol, clusters of needles; petroleum ether and methyl alcohol, square plates; acetone, triangular plates. The different crystal habits are all members of the hexagonal system.
On long standing at room temperature, or on heating for 24 hours at 105°, the crystals bleach, without losing their form. This fading is from the outer edge inward, showing a sharp line of demarcation between the unchanged carotene and the bleached or “achroo-carotene”. There is no change in weight, and the bleaching is accomplished as easily in nitrogen as in oxygen. Formerly hexagonal, the crystals are now isometric, denoting a radical change in the molecular structure. Achroo-carotene has no physiological activity.
Carotene is efficacious in curing the xerophthalmia, and allowing a resumption of growth, in vitamin A deficient rats. 0.005 mg. per day seems to be the practical minimum dose, although several individual rats have been able to grow on less. The effect of giving carotene continues for some time after the dosage has been stopped, and there seems to be a quantitative relationship between the amount given and the weight increase obtained, whether the carotene be given in one dose or in divided doses. 0.005 mg. allows a growth of at least 2 gm., the average growth increment being 3 to 5 gm. for this amount. This corresponds closely to Sherman's vitamin A unit.
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